The integration of wide-band high efficiency antennas into airframes especially at low frequencies is very difficult for two reasons: (1.) such antenna need to be large and cannot be protruding out of the airframe, and (2.) because most airframes are electrically conductive (aluminum or carbon-fiber), a conformational antenna printed on such surfaces have narrow bandwidth and low efficiency.
A search of issued U.S. patents in the field of aircraft antennas and related apparatus reveals U.S. patents related generally to the field of the present invention but which do not anticipate nor disclose the device of the present invention. The discovered U.S. patents relating generally to the present invention are discussed herein below.
U.S. Pat. No. 4,100,546 to Campbell et al. entitled “Airborne Antenna System Employing the Airframe as an Antenna” and U.S. Pat. No. 4,117,490 to Arnold et al. entitled “Inconspicuous Antenna System Employing the Airframe as an Antenna” each disclose a phase front homing system airborne antenna array employing portions of the airframe as two antenna elements. The invention provides an improved phase homing system antenna wherein the antenna elements are concealed or greatly reduced in profile. The antenna system comprises two substantially vertical sections of the airframe of the airplane. Included also are respective metallic toroid coils encompassing each of the vertical airframe sections and electromagnetically coupled thereto. The combination of each vertical section and its associated toroid coil comprises a respective antenna and corresponding terminals of the toroid coils comprise the radio frequency feed terminals to the respective antennas. The phase front homing system derives the desired sense of direction to a prescribed beacon transmitter by utilizing directly the phase difference at the two antenna elements.
U.S. Pat. No. 3,587,102 to Czerwinski entitled “Helicopter Skid Antenna” discloses a system of struts which are disposed perpendicular to the roll axis of a helicopter for supporting the landing skids thereof and are insulated from the helicopter fuselage. One of the struts has an antenna feed at its center, thereby the entire landing gear assembly functions as a folded dipole antenna or a loop antenna, depending on the operating frequency.
U.S. Pat. No. 2,510,698 to Johnson entitled “Radio Aerial, Particularly for Aircraft and Other Vehicles”, discloses an antenna design suitable for modern high speed aircraft, inter alia, wherein structural difficulties arise in fitting conventional (mast or wire) aerials external of the airframe. A mast type of aerial in the form of a wire stretched between two suitable external points of the host aircraft is subject to large aerodynamic forces such that it either becomes torn away from its supports, or due to its mechanical drag seriously interferes with the aerodynamic performance of the aircraft, besides being liable to a form of electrical interference known as precipitation static, as well as being a source of danger to the aircraft due to the possibility of fracture when flying at very high speeds approaching the speed of sound. Johnson provides a simple and unobtrusive radio aerial employing the metallic surface of the airframe structure to which it is applied and inductively couples the metallic surface to radio transmitting or receiving equipment whereby the surface is excited by the inductive coupling to effect radiation when radio signals are being transmitted or the inductive coupling is excited by the currents induced in the surface by electromagnetic radiations of a received radio signal. The inductive coupling may comprise one or more toroidal windings of wire which may either surround the metallic surface with the plane of the toroid or coil perpendicular to the axis of the surface or it may be concentrated at one or more points adjacent the metallic surface. In one application, the inductive coupling is mounted adjacent to the wing root, but external to the metal fuselage of the aircraft, whereby it sets up a magnetic field encircling the wing root or a portion thereof. One feature of the invention resides in associating the inductive coupling with two metallic structural parts whose longitudinal axes are mutually inclined so that the two parts act as crossed dipoles. When this feature is applied to an aircraft, the metallic wing and fuselage, or metallic portions of the fuselage and wing have an appropriate induction coil mounted adjacent to them in a manner which gives the required polar diagram of magnetic field.
None of the above listed U.S. patents disclose or suggest a zero weight antenna for aircraft utilizing conductive aircraft elements and method of the present invention. U.S. Pat. No. 4,100,546 to Campbell et al. and U.S. Pat. No. 4,117,490 to Arnold et al. describe an antenna realized by exciting the landing gear of a fixed-wing aircraft via inductive coupling. Neither Campbell nor Arnold reveal that the landing gears are electrically isolated from the aircraft body and biased against each other, which would be relevant to the present invention. Instead, both Campbell and Arnold claim to generate monopoles via inductive coupling. Similarly, U.S. Pat. No. 3,587,102 to Czerwinski describes a loop antenna realized by exciting the landing gear of a helicopter via direct electrical contact when the landing gear is electrically isolated from the body of the aircraft and via inductive coupling in the absence of electrical isolation. Czerwinski does not reveal that the body of the aircraft is biased against the landing gear to generate an antenna, which would be relevant to the present invention. U.S. Pat. No. 2,510,698 to Johnson proposes excitation of sections of the aircraft's airframe via inductive coupling at multiple locations to facilitate radiation and reception of radio waves. Johnson does not propose to isolate sections of the airframe from each other electrically and bias them against each other to form dipoles and monopoles, which is the essence of the present invention. Each of the above listed U.S. patents and published applications (i.e., U.S. Pat. Nos. 4,100,546; 4,117,490; 3,587,102; and 2,510,698) are hereby incorporated herein by reference.